1. Field of the Invention
The present invention relates to a method of determining at least one parameter that is characteristic of the angular distribution of light illuminating an object in a projection exposure apparatus.
2. Description of Related Art
To achieve an optimum projection result in a projection exposure apparatus, it is important that all structural directions of an object to be projected, in particular its horizontal and vertical structures, are imaged with optimum contrast. Such optimum contrast may not be achieved if the illumination of a pupil plane in the illuminating system deviates from its specified values, for example because it is asymmetrical and in particular astigmatic.
To be able to determine the projection quality of a projection exposure apparatus, the determination of the degree of homogeneity of the illumination of the pupil plane of the illuminating system is therefore necessary. This is a parameter that is characteristic of the angular distribution of the light illuminating the object to be projected.
According to a method known from commercially available products it is known to determine this parameter in that the illumination geometry is changed by inserting apertures in the beam path of the light source. Such a method is time-consuming.